1. Field
The present invention relates to a robot and a method of controlling balance thereof, and more particularly to a biped walking robot, which balances itself right and left on a two-dimensional space, and a method of controlling balance of the biped walking robot.
2. Description of the Related Art
In general, machines, which conduct motions similar to those of a human being using an electrical or magnetic action, refer to robots. Initial robots were industrial robots, such as manipulators or transfer robots, for work automation and unmanned operation in a production field, which perform dangerous work, simple repetitive work, or work requiring large force in place of a human being. Recently, biped walking robots, which have a joint system similar to that of a human being, live together with the human being in human working and living spaces, and walk with two feet, have been vigorously researched and developed.
Methods of controlling the walking of a biped robot include a position-based zero moment point (ZMP) control method, and a torque-based finite state machine (FSM) control method. The FSM control method means all methods, which use a torque control but do not use a ZMP control. In the FSM control method, finite states of the biped robot are defined in advance, and then the finite states of the biped robot are sequentially changed while walking, thus allowing the biped robot to properly walk.
The above FSM-based biped robot uses a limit cycle in order to balance itself on a two-dimensional space. The limit cycle means a trajectory movement, which forms a closed loop according to time on the two-dimensional space. In case that values of a function according to time form a random route in the closed loop as time infinitely goes by, the closed loop is referred to as the limit cycle (with reference to FIG. 1).
The limit cycle is divided into stable regions and unstable regions, and performs a nonlinear control. A region of the limit cycle, which is in a regular closed loop range, is referred to as a stable region, and a region of the limit cycle, which is not in the regular closed loop range but diverges radially or converges into one point, is referred to as an unstable region.
In order to allow the FSM-based biped robot to balance itself right and left on a two-dimensional space using the limit cycle, the maximum right and left moving distance of the robot should be reduced. However, the biped robot, which has a joint system similar to that of a human being, has an interval between two legs, i.e., a hip interval, due to actuators and several frames of hardware, and thus the radius of the limit cycle is increased according to this interval. When the radius of the limit cycle is increased, the right and left moving velocity of the robot is increased, and thus it is difficult to control ankles of the biped robot to balance the biped robot. Therefore, the feet of the biped robot (particularly, the soles of the feet) cannot parallel contact the ground, and thus the biped robot cannot achieve stable walking.